CN111138206B

CN111138206B - Amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam and preparation method thereof

Info

Publication number: CN111138206B
Application number: CN202010028587.2A
Authority: CN
Inventors: 王红洁; 蔡志新; 苏磊; 牛敏; 卢德
Original assignee: Xian Jiaotong University
Current assignee: Xian Jiaotong University
Priority date: 2020-01-11
Filing date: 2020-01-11
Publication date: 2021-04-20
Anticipated expiration: 2040-01-11
Also published as: CN111138206A

Abstract

The invention discloses amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam and a preparation method thereof. The preparation method is simple and easy to implement, has low requirements on equipment and can be used for mass production; the foam prepared by the method has light weight and wide absorption frequency band, and ensures the stability of the SiC nanowire continuous three-dimensional structure. As wave absorbing agent foam, when the thickness of the wave absorbing layer is 3.0mm, the foam obtains an effective absorption bandwidth of 10.1GHz (7.9-18GHz), covers the whole X and Ku wave bands, and is expected to realize industrial popularization and use.

Description

Amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam and preparation method thereof

Technical Field

The invention belongs to the field of wave-absorbing materials, and relates to amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam and a preparation method thereof.

Background

With the rapid development of modern information technology, the electromagnetic wave interference pollution is becoming more and more serious, and the electromagnetic wave absorbing material plays an increasingly important role in the fields of wearable intelligent electronics, national defense safety and the like. The traditional electromagnetic wave absorbing material is usually added with wave absorbing particle filler in a wave-transparent polymer matrix, so that the material has practical application value. These materials have high electromagnetic wave absorption performance, but are limited to specific frequency bands, and are a significant disadvantage in the face of electromagnetic wave interference pollution in more and more complicated frequency bands. In order to achieve broadband absorption, researchers have designed and prepared electromagnetic wave absorbers having multi-component and/or multi-layer structures. However, the preparation process of these materials is complicated, and the effective absorption band is difficult to reach 80% of the bandwidth of radar waves (2-18 GHz). By microstructural design, for example, by constructing high porosity and conductive structures, and using carbon nanostructure-based materials, a wider band of electromagnetic wave absorption is achieved. However, the minimum RL (greater than-30 dB) of these carbon-based electromagnetic wave absorbing materials is still too high, mainly due to impedance mismatch and lack of an efficient energy dissipation path due to their dielectric constant at the air/absorber interface. Therefore, it is an urgent need to prepare an electromagnetic wave absorbing material having both high absorption efficiency and a wide absorption band, but it is still a challenge.

Silicon carbide material, as a traditional dielectric wave absorber, has been widely used due to its tunable dielectric properties. However, more and more complex electromagnetic environments put higher requirements on wave-absorbing materials: not only needs to have wider absorption capacity, but also needs to meet the requirements of thin thickness, light weight and strong absorption. SiC nanowires are receiving increasing attention due to their low density, high aspect ratio, good mechanical flexibility, excellent thermal and chemical stability, and dielectric properties suitable for broadband absorption. Pure silicon carbide has the defects of small loss, low absorption strength and large addition amount in a matrix, and can not meet the requirements of the characteristics of thinness, lightness, width and strength. Therefore, researchers are working on the research and development of new wave absorbers.

The carbon material has the advantages of low density, stable structure and good electric and thermal conductivity, and has good application prospect in the field of wave-absorbing materials. The carbon doping is an effective way for improving the conductivity of the SiC nanowire material. The electromagnetic absorption performance of the SiC/C composite material can be greatly improved by combining the high-hole structure of the SiC/C composite material. This is because the special mesh conductive network optimizes the impedance matching and increases the microwave loss.

However, since the conventional method is to prepare the SiC/C composite material by coating carbon on the SiC nanowire, dispersing the SiC nanowire, and then freeze-drying the SiC nanowire, the SiC nanowire is inevitably damaged and aggregated due to a complicated preparation process, and a true continuous structure is difficult to form, so that the absorption performance of the SiC/C composite material is lower than expected. In addition, most of the existing carbon-based wave absorbers are still added in the matrix by more than 30 wt%, the effective absorption frequency band is still below 6GHz, and the light weight and broadband performance is still to be further improved. Therefore, how to prepare a light and broadband electromagnetic wave absorbing agent in a large scale by adopting low-cost raw materials and a simple synthesis process becomes a problem to be solved urgently in developing a novel wave absorbing material.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention designs a preparation method of amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam, and the preparation method is applied to the field of electromagnetic wave absorption, is easy to operate, has simple implementation conditions, and can be used for industrial production; the obtained special structure has low foam density, wide effective absorption frequency range and reliable structural stability.

In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:

the invention discloses amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam, which is formed by mutually overlapping SiC nanowires to form a continuous three-dimensional network structure with wide and adjustable aperture distribution range; wherein, the surface of the SiC nanowire is coated with an amorphous carbon layer; the SiC nanowire is 100-1000 mu m in length, 20-50 nm in diameter and 10-30 nm in thickness.

Further, when the thickness of the wave absorbing layer is 3.0mm, the continuous network structure foam constructed by the ultra-long three-dimensional SiC nanowire carbon coating has an effective absorption bandwidth of 10.1GHz, and can cover the whole X and Ku wave bands. Based on the characteristics, the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam can be widely applied as an electromagnetic wave absorbing material.

The invention also discloses a preparation method of the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam, which comprises the following steps:

1) uniformly mixing a carbohydrate material serving as a carbon source and a carbohydrate soluble liquid serving as a solvent to prepare a carbon source solution;

2) dispersing a carbon source solution into the SiC nanowire continuous three-dimensional network structure, enabling a carbon source to be uniformly coated on the surface of the SiC nanowire in the network structure, constructing nodes, obtaining a carbon source modified SiC nanowire continuous three-dimensional network structure film, and then drying;

3) and (3) designing the shape of the dried product obtained in the step (2), cutting and punching the dried product into a regular film, stacking the film into a block, placing the block in a highly controllable hot-pressing die, and carbonizing the block in an oxygen-free inert atmosphere to obtain the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam.

Preferably, in the step 1), the mass concentration of the carbon source solution is 0.5 wt% to 5 wt%.

Further preferably, the thickness of the amorphous carbon layer coated on the surface of the SiC nanowire in the SiC continuous three-dimensional network structure is regulated and controlled by controlling the concentration of the carbon source solution, so that the wave-absorbing performance and the mechanical property of the wave-absorbing foam of the SiC nanowire continuous three-dimensional network structure modified by the amorphous carbon are regulated and controlled.

Preferably, the saccharide is one or more selected from fructose, glucose and sucrose; the saccharide soluble liquid is selected from one or two of distilled water and dimethylformamide.

Preferably, in the step 2), a spraying method, a negative pressure dipping method or a filter pressing/suction filtration method is adopted to uniformly coat the carbon source solution on the surface of the SiC nanowire in the SiC nanowire continuous three-dimensional network structure.

Preferably, in the step 2), the drying treatment is carried out for 1-5 h at 40-140 ℃; in the step 3), the carbonization treatment temperature is 500-1300 ℃, and the heat preservation time is 1-5 h.

Preferably, in the step 3), the highly controllable hot-pressing mold is used for regulating and controlling the density of the final product, namely the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam, and the density is controlled to be 36-180 mg/cm³In the meantime.

The invention also discloses application of the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam as an electromagnetic wave absorbing material.

Preferably, when the thickness of the wave-absorbing layer is 3.0mm, the carbon-coated foam with the ultra-long three-dimensional SiC nanowire continuous network structure has an effective absorption bandwidth of 10.1GHz, and can cover the whole X and Ku wave bands.

Compared with the prior art, the invention has the following beneficial effects:

the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam disclosed by the invention is a continuous three-dimensional network constructed by SiC nanowires coated by amorphous carbon, an amorphous carbon layer can be used as a path for improving the electromagnetic loss on the surface of the SiC nanowires, and lap joints among the SiC nanowires can be constructed, so that the structural reliability of a three-dimensional continuous porous network structure is ensured. The amorphous carbon layer in the foam is continuously and uniformly distributed on the SiC nano-wire, and has good interface bonding with SiC. As wave absorbing agent foam, when the thickness of the wave absorbing layer is 3.0mm, the foam obtains an effective absorption bandwidth of 10.1GHz (7.9-18GHz), covers the whole X and Ku wave bands, and is expected to realize industrial popularization and use.

The preparation method of the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam disclosed by the invention can effectively avoid the damage of the traditional carbon coating process and the complicated steps of SiC nanowire dispersion to the structure, adopts a direct carbonization method, realizes the uniform coating of a carbon source through the fluidity of the carbon source at low temperature, can construct a lap joint point for the overlong SiC nanowire coated with the carbon source through the viscosity of carbon source liquid, and then carbonizes at high temperature to obtain a target product with adjustable carbon layer thickness, designable foam shape and adjustable foam density; the foam prepared by the method perfectly inherits the original SiC network structure, protects the integrity of the SiC nanowire continuous three-dimensional network structure, and obviously enhances the electromagnetic absorption performance and the mechanical property on the basis.

Drawings

FIG. 1 is a flow chart of example 1 of the method of the present invention;

FIG. 2 is an XRD (X-ray diffraction) pattern of the SiC nanowire continuous three-dimensional network structure wave-absorbing foam before and after amorphous carbon modification in embodiment 1 of the invention;

FIG. 3 is SEM photographs of SiC nanowire continuous three-dimensional network structure wave-absorbing foam before and after amorphous carbon modification in embodiment 1 of the invention; wherein a is before modification; b is after modification;

FIG. 4 is a TEM photograph and component analysis of the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam obtained in example 1 of the present invention; wherein a is a TEM photograph; b is component analysis; c is an interface;

fig. 5 is a wave-absorbing performance diagram of the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam obtained in embodiment 1 of the present invention.

Detailed Description

In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

The invention is described in further detail below with reference to the accompanying drawings:

the SiC nanowire continuous three-dimensional network structure used by the invention is prepared by adopting the technology disclosed in the invention patent ZL2016105664296, and the preparation method comprises the following steps:

20g of methyltrimethoxysilane, 5g of dimethyldimethoxysilane, 10g of deionized water and 10g of alcohol are mixed, 5mL of nitric acid is added as a catalyst, and stirring is carried out for 10min to obtain the siloxane sol. And then immersing the high-purity graphite carbon felt into the siloxane sol for 20min under negative pressure to crosslink siloxane in the carbon felt, taking out the carbon felt, and drying the carbon felt in a blast drying oven at 100 ℃ for 24h to obtain the carbon felt coated with the siloxane xerogel. And (3) placing the collected carbon felt in an air pressure furnace under the protection of 0.2MPa of argon, preserving the heat at 1450 ℃ for 2h for cracking, and cooling along with the furnace to obtain the ultra-long SiC nanowire on the graphite wall. The SiC nanowire has a length of 100-1000 μm, a diameter of 20-50 nm, and a density of 5mg/cm³～50mg/cm³。

Example 1

The preparation method provided by the first embodiment of the invention is shown in fig. 1, and the preparation process of the method is as follows:

selecting glucose as a carbon source, using distilled water as a solvent, and uniformly mixing the glucose and the distilled water in a certain proportion to form a carbon source solution with the concentration of 1 wt%; dispersing a carbon source solution into a SiC nanowire continuous three-dimensional network structure by a spraying method, enabling a carbon source to be uniformly coated on the surface of the SiC nanowire, constructing more nodes, obtaining a film constructed by the SiC @ carbon source, and drying at the temperature of 40 ℃ for 2 hours; and (3) designing the shape of the dried product, cutting and stamping, then overlapping the film into a block body, carrying out hot pressing treatment, carbonizing treatment in an oxygen-free inert atmosphere at the heat treatment temperature of 500 ℃ for 5 hours, and obtaining the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam.

XRD before and after amorphous modification of the SiC nanowire continuous three-dimensional network structure used in the embodiment is shown in figure 2, and the main component of the prepared foam is still SiC; in addition, a small amount of amorphous carbon is present. In fig. 3, a is a SiC nanowire continuous three-dimensional network structure of unmodified amorphous carbon; in fig. 3 b, a Scanning Electron Microscope (SEM) picture of the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam obtained by the method is shown, the material has a three-dimensional network structure which is communicated with each other, amorphous carbon uniformly coats the nanowire network, more nodes are constructed among the nanowires, and the integrity of the nanowire continuous network structure is ensured. FIG. 4 is a TEM image further illustrating the network structure of the foam and the uniform coating of amorphous carbon, consistent with the SEM image; in addition, it was further determined by elemental line scanning and high-power TEM that the three-dimensional carbon network was mainly a SiC nanowire core and an amorphous carbon shell, and that the core and the shell had good interfacial bonding.

The amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam prepared in this embodiment 1 is punched into a coaxial ring sample with an outer diameter of 7.00mm, an inner diameter of 3.00mm and a thickness of 2.00mm by using a special die, and is uniformly mixed with paraffin to prepare a wave-absorbing test sample. Electromagnetic parameters of the composite sample in the frequency range of 2-18GHz are tested by an Agilent E5071C vector network analyzer, and a reflection loss curve of the composite sample is calculated by MATLAB software according to a transmission line theoretical equation, as shown in FIG. 5. When the thickness of the wave-absorbing layer is 3.0mm, the Reflection Loss (RL) value of the composite material is-52.5 dB, the effective absorption bandwidth (RL < -10dB) reaches 10.1GHz (7.9-18GHz), and the whole X and Ku wave bands are covered. Therefore, the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam prepared by the invention shows good electromagnetic wave absorption performance.

Example 2

Selecting glucose as a carbon source, using distilled water as a solvent, and uniformly mixing the glucose and the distilled water in a certain proportion to form a carbon source solution with the concentration of 1 wt%; dispersing a carbon source solution into a SiC nanowire continuous three-dimensional network structure by a spraying method, enabling a carbon source to be uniformly coated on the surface of the SiC nanowire, constructing more nodes, obtaining a film constructed by the SiC @ carbon source, and drying at the temperature of 70 ℃ for 1 h; and (3) designing the shape of the dried product, cutting and stamping, then overlapping the film into blocks, performing hot pressing treatment, and carbonizing treatment in an oxygen-free inert atmosphere at the heat treatment temperature of 1000 ℃ for 1h to obtain the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam.

Example 3

Selecting glucose as a carbon source, using distilled water as a solvent, and uniformly mixing the glucose and the distilled water in a certain proportion to form a carbon source solution with the concentration of 0.5 wt%; dispersing a carbon source solution into a SiC nanowire continuous three-dimensional network structure by a spraying method, enabling a carbon source to be uniformly coated on the surface of the SiC nanowire, constructing more nodes, obtaining a film constructed by the SiC @ carbon source, and drying at the temperature of 140 ℃ for 1 h; and (3) designing the shape of the dried product, cutting and stamping, then overlapping the film into blocks, performing hot pressing treatment, and carbonizing treatment in an oxygen-free inert atmosphere at 1300 ℃ for 1h to obtain the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam.

Example 4

Selecting glucose as a carbon source, using distilled water as a solvent, and uniformly mixing the glucose and the distilled water in a certain proportion to form a carbon source solution with the concentration of 5 wt%; dispersing a carbon source solution into a SiC nanowire continuous three-dimensional network structure by a spraying method, enabling a carbon source to be uniformly coated on the surface of the SiC nanowire, constructing more nodes, obtaining a film constructed by the SiC @ carbon source, and drying at the temperature of 50 ℃ for 4 hours; and (3) designing the shape of the dried product, cutting and stamping, then overlapping the film into a block body, carrying out hot pressing treatment, carbonizing treatment in an oxygen-free inert atmosphere at the heat treatment temperature of 700 ℃, and keeping the temperature for 2 hours to obtain the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam.

Example 5

Selecting glucose as a carbon source, using distilled water as a solvent, and uniformly mixing the glucose and the distilled water in a certain proportion to form a carbon source solution with the concentration of 1 wt%; impregnating and dispersing a carbon source solution into a SiC nanowire continuous three-dimensional network structure by negative pressure, uniformly coating a carbon source on the surface of the SiC nanowire, constructing more nodes to obtain a film constructed by the SiC @ carbon source, and drying at the temperature of 80 ℃ for 2 hours; and (3) designing the shape of the dried product, cutting and stamping, then overlapping the film into blocks, performing hot pressing treatment, and carbonizing treatment in an oxygen-free inert atmosphere at 1100 ℃ for 1h to obtain the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam.

Example 6

Selecting sucrose as a carbon source, using distilled water as a solvent, and uniformly mixing the sucrose and the distilled water in a certain ratio to form a carbon source solution with the concentration of 1 wt%; dispersing a carbon source solution into a SiC nanowire continuous three-dimensional network structure by a filter pressing/suction filtration method, enabling a carbon source to be uniformly coated on the surface of the SiC nanowire, constructing more nodes, obtaining a film constructed by the SiC @ carbon source, and drying at the temperature of 100 ℃ for 1 h; and (3) designing the shape of the dried product, cutting and stamping, then overlapping the film into blocks, performing hot pressing treatment, and carbonizing treatment in an oxygen-free inert atmosphere at 900 ℃ for 2 hours to obtain the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam.

Example 7

Selecting sucrose as a carbon source, and dimethyl formamide as a solvent, and uniformly mixing the sucrose and the dimethyl formamide in a certain ratio to form a carbon source solution with the concentration of 1 wt%; dispersing a carbon source solution into a SiC nanowire continuous three-dimensional network structure by a spraying method, enabling a carbon source to be uniformly coated on the surface of the SiC nanowire, constructing more nodes, obtaining a film constructed by the SiC @ carbon source, and drying at the temperature of 50 ℃ for 2 hours; and (3) designing the shape of the dried product, cutting and stamping, then overlapping the film into a block body, carrying out hot pressing treatment, carbonizing treatment in an oxygen-free inert atmosphere at the heat treatment temperature of 600 ℃, and keeping the temperature for 2 hours to obtain the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam.

The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.

Claims

1. An amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam is characterized in that SiC nanowires are mutually overlapped to construct a three-dimensional continuous network structure with wide and adjustable aperture distribution range; wherein, the surface of the SiC nanowire is coated with an amorphous carbon layer;

the SiC nanowires are 100-1000 microns in length, 20-50 nm in diameter and 1-50 nm in thickness;

when the thickness of the wave absorbing layer is 3.0mm, the continuous network structure foam constructed by the ultra-long three-dimensional SiC nanowire carbon coating has an effective absorption bandwidth of 10.1GHz, and can cover the whole X and Ku wave bands.

2. The preparation method of the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam of claim 1, which is characterized by comprising the following steps:

1) uniformly mixing a carbohydrate material serving as a carbon source and a carbohydrate soluble liquid serving as a solvent to prepare a carbon source solution; wherein:

the saccharide is one or more selected from fructose, glucose and sucrose; the mass concentration of the carbon source solution is 0.1-10 wt%; the saccharide soluble liquid is one or two of distilled water and dimethyl formamide;

2) dispersing a carbon source solution into the SiC nanowire continuous three-dimensional network structure, coating the carbon source on the surface of the SiC nanowire, forming a lap joint between adjacent nanowires to obtain a film constructed by the SiC/carbon source, and then drying;

3) carrying out shape design on the dried product obtained in the step 2), cutting and stamping the dried product into a preset shape, superposing the preset shape into a block, and placing the block in a high-temperature oxygen-free inert atmosphere for carbonization treatment to obtain amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam; wherein the carbonization treatment temperature is 500-1300 ℃, and the heat preservation time is 1-5 h.

3. The method for preparing the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam according to claim 2, wherein the wave-absorbing performance and the mechanical property of the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam are regulated by controlling the mass concentration of a carbon source solution to regulate the thickness of an amorphous carbon layer coated on the surface of the SiC nanowire in the SiC nanowire continuous three-dimensional network structure.

4. The method for preparing the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam according to claim 2, wherein in the step 2), a carbon source solution is uniformly coated on the surface of the SiC nanowire in the SiC nanowire continuous three-dimensional network structure by adopting a spraying method, a negative pressure impregnation method or a filter pressing/suction filtration method.

5. The preparation method of the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam according to claim 2, wherein in the step 2), the drying treatment is carried out at 40-140 ℃ for 1-5 h.

6. The method for preparing the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam according to claim 2, wherein in the step 3), a highly controllable hot-pressing mold is adopted to regulate and control the density of a final product, namely the amorphous carbon modified SiC nanowire continuous three-dimensional network structure wave-absorbing foam, and the density is controlled to be 36-180 mg/cm³In the meantime.